Unwanted line break using echo and cat

Question

I'm trying to add a line at the beginning of a file, using

echo 'time/F:x1:x2' | cat - file.txt>newfile.txt

But this produces line breaks at each line in the new file (except for after the added 'time/F:x1:x2' line). Any ideas on how to avoid this?

wait, what do you mean "produces line breaks at each line"? what does the input file look like and what does the output file look like? — glenn jackman, Mar 18 '14 at 18:32
Sorry, this was badly phrased, I posed a new question http://stackoverflow.com/questions/22502013/unwanted-empty-lines-using-echo-and-cat @glennjackman — pengwing, Mar 19 '14 at 09:55

score 2 · Answer 1 · answered Mar 18 '14 at 17:46

2

Use -n to disable the trailing newline:

echo -n 'time/F:x1:x2' | cat - file.txt > newfile.txt

There are other ways, too:

sed '1s|^|time/F:x1:x2|' file.txt > newfile.txt

answered Mar 18 '14 at 17:46

devnull

2

Or use `printf`: `printf "%s" 'time/F:x1:x2 | ... ` – Digital Trauma Mar 18 '14 at 18:32
Let me clarify: I should have written "empty lines", not "line break". So if my input is `line1 {linebreak} line2 {linebreak} line3` my output will be `time/F:x1:x2 {linebreak} line1 {linebreak} empty line {line break} line2 {line break} empty line {line break} line3` I want the first line break after time/F:x1:x2, but not the empty lines. – pengwing Mar 18 '14 at 20:59

score 1 · Answer 2 · answered Mar 18 '14 at 18:31

1

How about

{ echo 'time/F:x1:x2'; cat file.txt; } >newfile.txt

or

sed '1i\
time/F:x1:x2' file.txt > newfile.txt

answered Mar 18 '14 at 18:31

glenn jackman

I think the `{ echo …; cat; }` compound command would still produce the unwanted newline. – kojiro Mar 18 '14 at 18:34
Shouldn't that be `echo -n`? +1 for the use of the `{}` command grouping to make this more readable – Digital Trauma Mar 18 '14 at 18:34
The question is ambiguous: "I'm trying to add a line at the beginning of a file" – glenn jackman Mar 18 '14 at 18:54

score 0 · Answer 3 · answered Mar 18 '14 at 18:35

0

Actually you don't even need the echo and pipe if you're using bash. Just use a herestring:

<<< 'time/F:x1:x2' cat - file.txt > newfile.txt

answered Mar 18 '14 at 18:35

kojiro

This'll insert a newline, same as `echo` without `-n`, no? – Digital Trauma Mar 18 '14 at 18:37
1

Hmm, suppose it does, at that. I'll leave it here until OP clarifies *produces line breaks at each line*. – kojiro Mar 18 '14 at 18:41

3 Answers3